Possible Clues:

• Parts of a day (Abbr.)
• MLB blasts
• There are 24 in a day (Abbr.)
• Day parts: Abbr
• 60-min. intervals
• MLB stats
• Time sheet nos
• Appt. book divisions
• PO door posting
• Personnel depts., and what the personnel in 20-, 31-, 40- and 50-Across have in common